I admit I’m a snob when it comes to pinto and refried beans. I never really care for the taste of whole pintos in a can, and I just hate canned refried beans. It reminds me of dog food. That whole “slurp” as it comes out of the can. Yuck! I think I was spoiled by my mom. She is very good at cooking refried beans.
DO NOT REMOVE THE JUICE. It will look like you’re going to end up having soupy beans, but as it cools it become less and less runny. If you remove the juice you will have sticky clumps of beans which is not very good.
Come back after the butter has melted (just a few minutes). Then take out your potato masher and smash the hell out of those beans.